ADENOSINE RECEPTOR-MEDIATED STIMULATION OF INTRACELLULAR CALCIUM IN ACUTELY ISOLATED ASTROCYTES

The characteristics of adenosine receptors found in glial fibrillary a cid protein (GFAP)-positive astrocytes acutely isolated from the cereb ral cortices of 4- to 12-day old rats were examined by evaluating the effects of adenosine and its analogues on intracellular calcium levels . First these effects were compared with those seen in primary astrocy tic cultures, and it was found that acutely isolated astrocytes showed much greater sensitivity to adenosine than their cultured counterpart s. Then, the adenosine evoked calcium responses in acutely isolated ce lls were evaluated under various conditions. The responses to adenosin e were not inhibited by papaverine, an uptake blocker, or by removal o f extracellular calcium. U73122, a phospholipase C inhibitor, was able to completely inhibit the adenosine response. The receptor inhibitor 3-isobutyl-1-methylxanthine inhibited the calcium response to adenosin e, providing evidence that the response is nor coupled to the xanthine -insensitive A(3) receptor. The stimulatory action of NECA, a non-sele ctive analogue, was blocked neither by the A(2A)-selective receptor an tagonist 8-(3-chlorostyryl) caffeine nor by the A(1)-selective recepto r antagonist 8-cyclopentyl-1,3-dipropylxanthine. The A(2B) receptor an tagonist alloxazine, however, was able to completely inhibit the incre ase in intracellular calcium produced by NECA. Taken together, these d ata suggest that the adenosine-evoked calcium response in acutely isol ated astrocytes is coupled to the A(2B) receptor. (C) 1998 Elsevier Sc ience B.V. Ail rights reserved.